北祁连造山带西段车路沟岩体U-Pb年代学、地球化学特征及岩石成因

车路沟岩体位于北祁连造山带最西端,岩石类型以英云闪长玢岩和闪长玢岩为主。本次对英云闪长玢岩进行U-Pb年代学研究,获得加权平均年龄为(462.1±3.8)Ma,表明岩体形成于中奥陶世。岩石地球化学分析结果显示,英云闪长玢岩中SiO_2含量60.37%～66.73%,Al_2O_3含量15.65%～16.45%,Na_2O/K_2O值7.47～9.96,A/CNK为0.90～1.00,属中酸性岩系列,显示相对富钠、低钾的特征, A/CNK=0.90～1.00,属于准铝质低钾钙碱性系列;稀土总量较低(33.40×10~(-6)～39.27×10~(-6)),LREE/HREE值为3.95～6.51,在稀土元素配分图解上呈现出右倾特征;δEu值1.23～1.49之间,呈现Eu呈正异常特征;在微量元素原始地幔标准化图解上,显示富集Ba、Sr,亏损Nb、Ti、Yb高场强元素的特征。对车路沟岩体地质、地球化学特征与产出背景的全面分析,认为其为奥陶纪祁连洋持续向华北板块俯冲,诱使俯冲洋壳部分熔融形成的埃达克岩。     

福建政和夏山铅锌矿成矿时代研究及讨论

福建政和夏山铅锌矿是福建省于20世纪50年代发现的大型铅锌矿,其成因类型长期存在分歧。前人多将其归为沉积-改造型铅锌矿床,即矿层在新元古代由含矿热水沉积形成,燕山期岩浆侵入仅对其进行了改造和富集;但也有部分学者认为夏山铅锌矿是受燕山期铜盆庵正长花岗岩侵入作用影响所形成的矽卡岩型铅锌矿床。本文通过对夏山铅锌矿矿区精细的地质调查表明,夏山铅锌矿体的分布及形态与矿区内花岗斑岩密切相关,铜盆庵岩体对夏山铅锌矿的影响表现在后期的叠加、富集作用。为精确厘定夏山铅锌矿成岩成矿时代,文章对夏山铅锌矿矿区内与成矿相关的花岗斑岩进行了精确的锆石La-ICP-MS U-Pb定年工作。测试结果表明矿区花岗斑岩的侵入时代为(173.0±1.7)Ma,要早于铜盆庵岩体(155～150 Ma),而夏山铅锌矿则形成于(173±1.7)Ma(燕山早期)。这一成矿时代与赣东北地区主要的铜、银、铅锌多金属矿的成矿时代较为一致,表明武夷山地区对华南中生代第一期爆发式成矿作用亦有积极响应,具有早燕山期铜、银、铅锌多金属矿的成矿潜力。而结合前人研究成果,将武夷成矿带北段成矿期次划分为173 Ma和90～125 Ma两个重要的成矿期次,这一研究结果对武夷山成矿带进一步开展隐伏、叠加矿床的找矿工作及成矿规律研究具有重要意义。     

桂东北姑婆山岩体矿物学和年代学特征及其成岩成矿意义

为揭示桂东北姑婆山一带花岗岩的成岩成矿特征,本文对姑婆山岩体进行了黑云母矿物化学成分分析和锆石U-Pb年代学研究。花岗岩中黑云母化学成分分析结果表明：黑云母具有富铁镁、贫钙钠的特征,w（TFeO）为26.78%~31.06%、w（MgO）为2.98%~6.60%,且w（TFeO）与w（MgO）呈明显的负相关性,说明其结晶过程中主要发生了Fe²⁺←→Mg²⁺的置换反应;黑云母的含铁指数为0.68~0.84,属于高铁黑云母,氧逸度为-17.0~-15.5,结晶温度为680~705℃,平均为695℃;黑云母的全铝压力计显示黑云母结晶的压力为69~179 MPa,平均为115 MPa,对应的侵位深度相当于2 621~6 755 m,平均深度为4 331 m。年代学分析结果显示,采自姑婆山岩体的两个代表性花岗岩样品形成年龄分别为（162±3）和（163±2）Ma,为燕山早期,与华南中生代大规模岩浆-成矿作用时代一致。综合上述分析,姑婆山岩体形成于较高温度、低氧逸度、较浅的环境,显示出良好的锡成矿性,具有良好的找矿前景。     

吉东南地区五女峰岩体锆石U-Pb年代学、岩石地球化学特征及其构造意义

五女峰岩体位于通化地区集安市,大地构造位置上处于鸭绿江—图们江断裂北侧,其岩性为碱长花岗岩。为确定其侵位时代和探讨大地构造环境,对五女峰岩体进行了系统的岩石学、矿物学和年代学研究。LA-ICP-MS锆石U-Pb测年结果显示,其加权平均年龄为（110.50±1.60） Ma,侵位时代为早白垩世晚期。岩体具有高硅、富碱、富铝和低钛的特点,属于高钾钙碱性系列;A/CNK值为0.98~1.00,为准过铝质岩石;固结指数（I_S）为0.80~3.20,反映了该岩体经历了高程度分异演化作用;δEu为0.05~0.37,具较强的Eu亏损,LREE/HREE和（La/Yb）_N值分别为7.13~24.68和7.01~39.20,显示轻重稀土元素分馏明显,且具有轻稀土元素富集、重稀土元素亏损的特点。五女峰岩体呈现明显富集大离子亲石元素（LILE） Rb、K、Th、U,略富集高场强元素（HFSE） Nd、Sm、Zr、Hf,以及明显亏损P和Ti的特征。综合岩石矿物学、年代学、岩石地球化学特征及区域地质资料,五女峰岩体属于A型花岗岩,形成于后造山的伸展体制环境下。     

滇西加里东期平河复式花岗岩体锆石U-Pb年龄、Hf同位素特征及其风化壳型稀土矿成矿认识

加里东期平河复式花岗岩体位于滇西保山地块西部边缘,其岩石类型主要为二长花岗岩、似斑状二长花岗岩。平河复式花岗岩体主量元素显示岩石全碱（w（K₂O+Na₂O））值分别为6.89%和7.44%,K₂O/Na₂O值分别为1.59和2.65,铝饱和指数（A/CNK）值分别为1.58和1.76,里特曼指数（σ）分别为1.65和1.73;微量稀土元素显示岩石总体上富集Rb、Th等大离子亲石元素,亏损Ta、Nb等高场强元素,轻稀土元素富集,LREE/HREE值分别为1.40和6.43,具低-中等负铕异常（δEu=0.16和0.75）。2件花岗岩样品的锆石U-Pb年龄变化于478~476 Ma,表明这些花岗岩类侵位于早奥陶世;2件样品38颗锆石测点的ε_Hf（t）值显示较大的变化范围,对应的Hf同位素地壳模式年龄集中在2.2~1.7 Ga。这些地球化学特征显示平河复式花岗岩体属钙碱性过铝质S型花岗岩,为泛非运动构造碰撞后应力松弛阶段产物,其形成可能与滇西地区原特提斯地史阶段地块挤压碰撞、裂离过程密切相关。在大团山地区,该期岩体中首次发现含稀土矿物——锰铁铈氧化物,其对全风化岩体稀土氧化物总量贡献最大;岩体风化壳稀土氧化物总量（REO）总体不高,为279.05×10^-6~791.77×10^-6,总体富集Y、La、Ce元素,局部轻稀土元素Nd富集,重稀土镝氧化物配分较高,为2.30%~4.62%。大团山稀土矿点的发现,表明滇西加里东期花岗岩亦有寻找花岗岩风化壳型稀土矿的潜力。     

Zircon U–Pb dating of gabbro and diorite from the Bato pluton,northeast Japan

To constrain the timing of the tectonothermal events and formation process of a plutonic suite, U–Pb dating was carried out by laser ablation inductively coupled plasma mass spectrometry combined with cathodoluminescence imaging on zircon grains extracted from the Bato pluton, northern Yamizo Mountains, Japan. The Bato pluton consists of gabbro and diorite. Zircon grains separated from a gabbro sample had a unimodal ²³⁸U–²⁰⁶Pb age (105.7 ±1.0 Ma). It was interpreted as the solidification age of the gabbro. Cathodoluminescence observation showed that the zircon grains from a diorite sample were characterized by anhedral cores, oscillatory zoned mantles, and dark rims. The ²³⁸U–²⁰⁶Pb age of the anhedral cores ranged from 2 165 Ma to 161 Ma, indicating the assimilation of surrounding sedimentary rocks. The ²³⁸U–²⁰⁶Pb ages of the oscillatory zoned mantles and dark rims are 109.0 ±1.3 Ma and 107.7 ±1.3 Ma, respectively. Observation under polarizing microscopy suggests that the anhedral cores occurred before plagioclase and hornblende, and the oscillatory zones around the anhedral cores had crystallized at the same time as the crystallization of biotite. Moreover, the dark rims formed at the same time as the crystallization of quartz and K‐feldspar. The formation process of the gabbro‐diorite complex in the Bato pluton was inferred as follows. (i) A mafic initial magma intruded into Mesozoic sedimentary rocks, and the assimilation of these sedimentary rocks led to geochemical variation yielding a dioritic composition. Subsequently, plagioclase and hornblende of the diorite were crystallized before 109.0 ±1.3 Ma. (ii) Biotite crystallized in the middle stage around 109.0 ±1.3 Ma. (iii) Quartz and K‐feldspar of the diorite were crystallized at 107.7 ±1.3 Ma. The gabbroic magma solidified (105.7 ±1.0 Ma) after solidification of the diorite.     

Spatial distribution of the apatite fission‐track ages in the Toki granite,central Japan: Exhumation rate of a Cretaceous pluton emplaced in the East Asian continental margin

The Cretaceous Toki granitic pluton of the Tono district, central Japan was emplaced in the East Asian continental margin at about 70 Ma. The Toki granite has apatite fission‐track (AFT) ages ranging from 52.1 ±2.8 Ma to 37.1 ±3.6 Ma (number of measurements, n = 33); this indicates the three‐dimensional thermal evolution during the pluton's low‐temperature history (temperature in the AFT partial annealing zone: 60–120 °C). The majority of the Toki granite has a spatial distribution of older ages in the shallower parts and younger ages in the deeper parts, representing that the shallower regions arrived (were exhumed) at the AFT closure depth earlier than the deeper regions. Such a cooling pattern was predominantly constrained by the exhumation of the Toki granitic pluton and was related to the regional denudation of the Tono district. The age–elevation relationships (AERs) of the Toki granite indicate a fast exhumation rate of about 0.16 ±0.04 mm/year between 50 Ma and 40 Ma. The AFT inverse calculation using HeFTy program gives time‐temperature paths (t–T paths), suggesting that the pluton experienced continuous slow cooling without massive reheating since about 40 Ma until the present day. A combination of the AERs and AFT inverse calculations represents the following exhumation history of the Toki granite: (i) the fast exhumation at a rate of 0.16 ±0.04 mm/year between 50 Ma and 40 Ma; (ii) slow exhumation at less than 0.16 ±0.04 mm/year after 40 Ma; and (iii) exposure at the surface prior to 30–20 Ma. The Tono district, which contains the Toki granite, underwent slow denudation at a rate of less than 0.16 ±0.04 mm/year within the East Asian continental margin before the Japan Sea opening at 25–15 Ma and then within the Southwest Japan Arc after the Japan Sea opening, which is in good agreement with representative denudation rates obtained in low‐relief hill and plain fields.     

胶东早白垩世高镁闪长岩类的发现及其构造背景

胶东地区发育大规模早白垩世壳幔混合源花岗岩类,但一直未发现与花岗岩类相关的独立的幔源侵入体,给深入理解早白垩世壳幔演化带来了困惑。胶东的柳林庄和夏河城岩体以往被认为是三叠纪闪长岩类,本文在详细的野外地质工作基础上,通过年代学、岩石地球化学、同位素地球化学分析,发现这2个岩体为早白垩世高镁闪长岩。样品的SiO₂含量在53.29%~62.54%之间,MgO含量为3.60%~8.10%,Mg^#主要介于0.47~0.68之间;富集Ba、Rb、K等大离子亲石元素,亏损Nb、Ta、Zr等高场强元素;初始⁸⁷Sr/⁸⁶Sr值为0.7082~0.7083,与地幔平均值接近;ε_Nd（t=113Ma）值很低（-20.5~-16.8）,与胶东地区的基性脉岩同位素组成一致。2个岩体相比而言,柳林庄岩体富K₂O、Fe₂O₃^T,REE、LILE、HFSE含量较高,而MgO、Ni和Cr含量偏低。3件样品的锆石LA-ICP-MS U-Pb同位素加权平均年龄值分别为120.1±1.6Ma、118.3±1.7Ma和122.3±4.0Ma,与壳幔混合源的伟德山型花岗岩及胶东金矿的成岩、成矿时代一致,指示他们形成于统一的地球动力学背景。高镁闪长岩的地球化学特征介于高镁埃达克岩与赞岐岩及埃达克岩与Piip型高镁安山岩之间,指示其形成于古太平洋板块俯冲的地幔楔环境,为富集岩石圈地幔部分熔融的产物。夏河城岩体的岩浆直接来源于含角闪石的富集岩石圈地幔源区,而柳林庄岩体岩浆源区为含金云母的岩石圈地幔并且在岩浆上侵过程中混染了部分地壳物质。     

南秦岭佛坪地区五龙花岗质岩体的地球化学特征及成因研究

南秦岭印支期五龙岩体侵位于中元古代佛坪群变质岩,在岩体南部发育一些暗色包体.它们和寄主黑云母花岗闪长岩界限或截然,或呈过渡关系.通过对五龙岩体的地球化学、锆石LA-ICP-MS U-Pb年代学研究结果表明,寄主黑云母花岗闪长岩表现出明显埃达克岩的地球化学特征:强烈亏损重稀土元素Yb(0.33×10-6～0.96×10-6)和Y(4.77×10-6～11.2×10-6);富集Sr(643×10-6～1115×10-6),Ba(775×10-6～1386×10-6);高Sr/Y(57.8-160)和Y/Yb(11.0-14.3)比值,不发育Eu异常(δEu=0.70～0.83),表明其源区是以石榴石士角闪石为主,很少或没有斜长石.暗色包体表现出高Mg(4.15%～8.13%),Cr(14.8×10-6～371×10-6),Ni(20.0×10-6～224×10-6)和Nb/Ta(15.40～21.9),暗示其起源于地幔底侵岩浆.锆石LA-ICP-MS U-Pb定年年龄为:225.3Ma±6 Ma,应为五龙黑云母花岗闪长岩的侵位年龄.综合分析五龙埃迭克质黑云母花岗闪长岩可能是由于幔源岩浆底侵于壳幔边界,诱发增厚的基性下地壳达到含角闪石的榴辉岩相或麻粒岩相发生部分熔融形成埃迭克质岩浆,它的形成可能代表了印支期秦岭造山带后碰撞造山阶段勉略洋俯冲板块的断离作用.     

东秦岭灵山岩体岩石谱系单位类埃达克质花岗岩及其成因和构造环境意义

灵山岩体地处东秦岭造山带的南秦岭构造带的桐(柏)-商(城)断裂两侧。根据内部接触关系和结构等方面的差异,将灵山岩体划分为主侵入期四个单元和补充期三个独立单元。该花岗岩属高硅碱富钾贫钙低镁碱性系列,稀土元素总量较高且具右倾海鸥式配分模式,微量元素具富集大离子亲石元素K、Rb、Ba等和亏损高场强元素Zr、Hf、P、Ta、Nb、Ti等特点;是具有某些I型(类埃达克质)花岗岩地球化学特征的同熔性S型花岗岩,形成于弧-陆碰撞造山后(非造山)的拉张环境。